1. Field of the Invention
The present invention relates to optimizing radio link control unacknowledged-mode protocol data unit headers, for example, to better support packet switched voice transmissions or transmission of other real time packet switched services over Wideband CDMA air interface.
2. Description of the Related Art
With Voice-over-IP (VoIP) there are typically several different radio link control (RLC) Service Data Unit (SDU) sizes. FIG. 1a illustrates a measured example distribution for a 12.2 kbit/s adaptive multi rate (AMR) voice codec. The voice codec itself produces equal size packets but a robust header compression (ROHC) produces variable size SDUs. In order to optimize the RLC overhead, for the example in FIG. 1a, the following RLC Protocol Data Unit (PDU) sizes could be selected: 11, 15, 36, 40 and 98 octets. RLC PDU sizes of 11 and 36 octets may be used for the most frequent RLC SDU sizes, silence indicator (SID) and speech frames, respectively. RLC PDU sizes of 15 and 40 octets may be used for several, less frequent, RLC SDU sizes. It is noted that there are quite significant amounts of RLC SDUs which are 2 octets smaller than the RLC PDU sizes, 13 and 38 octets (SDU sizes), respectively.
For a RLC SDU which is two octets smaller than the RLC PDU, the beginning of the RLC SDU is indicated with special length indicator (LI), where LI=1111100 or LI=0000000 if the previous RLC SDU was also two octets smaller than the RLC PDU. Therefore, there is no room to indicate the end of the RLC SDU and that has to be indicated in the next RLC PDU with LI=0000000. As such, if the next PDU is lost, a receiver cannot be sure whether the RLC SDU was completely there or not.